The variability of hydrogen isotope ratios (H/D ratios) in plant material is not well understood. This is supposedly caused by interacting climatic factors (H/D ratio of precipitation) and physiological influences on the internal D distribution of metabolites. This project aims at isolating physiological influences using D NMR. Specifically, plants' responses to growth under increased CO2 and other parameters will be examined. The methodology to obtain well resolved D NMR spectra of glucose has been developed. Preliminary results on glucose from spinach indicate that the intensity of the D signal in the pro-R position of C(6) (C(6)-DR) increases by approximately 12% in plants grown under increased CO2. The intensity of C(4)-D is reduced by approximately 20% upon growth under increased CO2 and low light levels. The effects are localized to these positions and seem not to influence each other. The near-term goal of this project is to reproduce the observed effects with a larger number of plants. Experiments are planned to test hypothyses about the cause of the effects and to observe such effects in natural plant material. The long term goal of this project is to use internal D distributions to monitor plants' responses to atmospheric CO2 increase. Several other applications of the technique (e.g., in plant breeding programs) are conceivable.